The present invention relates to a conveyor having a mechanism for driving an endless chain, which is used for driving and optionally also for supporting the article-supporting parts of the conveyor. The mechanism comprises a drive belt that engages and drives on a number of wheels on the chain. By driving on the periphery of the rotating wheels instead of directly on the chain itself, the force between the drive belt and the point of engagement with the chain is halved whereby the construction may be made substantially lighter.
In a preferred embodiment, the drive mechanism is displaceable arranged with respect to the stationary part of the conveyor along a path having an angle with the transport direction of the conveyor so that the reactive force on the drive mechanism caused by the driving force applied to the wheels causes the drive mechanism to be biased towards the wheels whereby the normal force from the mechanism on the wheels is self-adjusting, depending on the magnitude of the required drive force.
The present invention further relates to the drive mechanism as such according to the preferred embodiment.
Drive chains for conveyors are known in the art to be driven with various drive mechanisms. The best known is probably a sprocket wheel drive in which the teeth of a sprocket wheel engage with openings in the chain. The sprocket wheel drive requires an equidistant distribution of the openings in the chain which may cause problems when the chain becomes worn and in all cases presents an inconvenience when using chain links of a standard length to construct a chain of a particular length, because any difference between the required length of the chain and an integer multiple of the standard length must be carefully distributed between all the links in order to match the chain and the sprocket wheel. Furthermore, the links must be of an adjustable length and the sprocket wheel drive tends to produce noise in operation. A chain to be driven by a sprocket wheel drive is disclosed in GB-A-333707.
Another type of drive mechanism is a friction drive in which a wheel or an endless belt engages a substantially straight closed surface of the chain as disclosed in EP-A-0532137 and in EP-A-0768252. The endless belt is normally biased into engagement with the chain by a couples of springs or the like as disclosed in EP-A-0532137. The present invention has in particular the advantages with respect to the known art:
The drive mechanism engages with the periphery of wheels mounted on the chain, whereby the drive force transmitted between the drive mechanism and the chain is halved and the mechanism can be made of a lighter construction,
the drive mechanism is self-adjusting with respect to the normal force on the chain, whereby unnecessary wear on the contact parts of the belt and the wheels is avoided during operational conditions where the required drive force and thus the required normal force is low, and
the drive mechanism is self-balancing with respect to the distribution of normal force among the wheels with which the drive mechanism is in engagement.
Thus, the present invention relates to a conveyor comprising
a stationary track part defining a closed conveyor path,
a flexible elongated drive chain including a plurality of consecutive links being pivotally interconnected to adjacent links so as to form a closed loop that is movable along said conveyor path within the track part,
a plurality of drive wheels being mounted on the drive chain, the rotation axes of the drive wheels being substantially parallel and perpendicular to the elongated direction of the chain, and
at least one drive mechanism arranged along the stationary track part and comprising a drive means for engaging and applying a driving force on the periphery of at least one of said drive wheels in the direction of movement of the chain, and support means for engaging said drive wheel(s) being in engagement with the drive means on the opposite side of the periphery of the wheel(s) and applying a reactive force on the wheel(s) of a magnitude and direction as the driving force.
It is preferred that the support means comprises a stationary side face on which the wheels rolls, although a support means comprising a driven endless belt moving along or opposite to the chain could be employed according to the invention.
The drive wheels are preferably arranged substantially equidistantly along the elongated direction of the chain and are of substantially identical diameter. The wheels may along the remaining part of the serve as guide wheels for guiding the chain between sides of the track part along the path of the chain or as supporting wheels for at least partly supporting the weight of the chain on a track part, depending on the orientation of wheel axes being vertical or horizontal.
The drive mechanism further comprises a drive unit, such as an electrical motor, for driving the drive mechanism, and a control unit for controlling the torque and the angular velocity of the motor.
The drive mechanism and the support means may be mounted with a well-defined constant opening for the wheels defined there between, but in preferred embodiments of the present invention, the drive mechanism comprises biasing means arranged for biasing the drive means towards the drive wheels so as to exert a normal force on the drive wheels of a sufficient magnitude to prevent slippage between the wheels and the drive means and between the wheels and the support means, the support means being suitable for exerting a reactive force on the wheels to counteract the normal force. Such biasing means may be e.g. springs, pneumatic cylinders or the self-adjusting biasing device of the present invention being disclosed below in details.
The drive mechanism may be arranged so that the mechanism engages one wheel at a time and the inertia of the chain and the conveyor makes the movement of the conveyor continuous, but it is for the smoothness of operation and stresses on the driving part preferred that the drive wheels and the at least one drive mechanism are arranged so that there is constantly at least one of the drive wheels in engagement with a drive mechanism during operation of the conveyor.
In the most preferred embodiment the drive means comprises an endless belt engaging at least two consecutive drive wheels simultaneously, preferably from 3 to 12 wheels and in the most preferred embodiment 7 wheels.
When more that one wheel is engaged, it is of importance that the biasing means are arranged for providing substantially identical normal forces on the drive wheels being in engagement with the drive means so that the wear is equally distributed and so that the drive means does not slip on one or more of the wheels on which the normal force is lower than required.
A preferred solution to the normal force distribution is that the drive means are pivotally arranged with respect to the track part about an axis being parallel to the rotation axes of the drive wheels so as to distribute the normal force exerted by the biasing means equally between the drive wheels engaged by the drive means.
The self-adjustment of the normal force so that the force is sufficient to prevent slippage between the surfaces but is low enough to prevent unnecessary wear and stress on the contact parts is achieved when the biasing means is constituted by a frame part on which the drive means are arranged, the frame part being displaceable arranged with respect to the track part along a tensioning path having an angle with the direction of movement of the chain so that the reactive force on the drive means from applying the driving force to the drive wheel(s) will tend to bias the drive means towards the drive wheels.
The self-adjustment according to the present invention may be combined with another biasing means, such as one or more pre-tensioned springs. However, it is for the simplicity of the device preferred that the self-adjustment is the sole means of biasing the drive mechanism towards the wheels, and in order to make such self-adjustment workable, the friction coefficient between the drive wheels and the drive means as well as the friction coefficient between the drive wheels and the support means should be greater than tangents to the angle between the tensioning path and the direction of movement of the chain. In particular, the friction coefficients should be to 1.5 times the tangents to said angle, and preferably be in the range from 1.1 to 1.3 times the tangents to said angle.
The surfaces of the drive means and the support means engaging the drive wheels may in order to prevent slippage between the wheels and the drive means and between the wheels and the support means be equipped with a friction enhancing material, such as a natural or synthetic rubber.
According to a further aspect, the present invention also relates to a drive mechanism as such being self-adjusting with respect to the magnitude of the normal force on the drive chain of a driven conveyor, said drive mechanism comprising
a drive means for engaging and applying a driving force to a drive chain of the conveyor, the drive mechanism comprises
biasing means arranged for biasing the drive means towards the drive chain so as to exert a normal force on the drive chain of a sufficient magnitude to prevent slippage between the chain and the drive means,
wherein the biasing means is constituted by a frame part on which the drive means are arranged, the frame part being displaceable arranged along a tensioning path having an angle (xcfx86) with the direction of movement of the drive chain so that the reactive force on the drive means from applying the driving force to the drive chain will tend to bias the drive means towards the drive chain.